The present invention relates to a sighting device such as a gun sight, usable under all light conditions, day or night.
Optical sighting devices in which an aiming mark or a graticule is superimposed on the target as seen through an optical element such as a beam splitter have become very popular in recent years. The user of such a sight need no longer align front and rear sights first between themselves and then with the target as in standard rifle sights, nor does he have to cope with the limited field of telescopic sights and their focusing problems. In these optical sights a mark or graticule serves as aiming point, and the user simply moves the gun until the aiming point, appearing at infinity as superimposed on the target area, is centered on the target (or leads it by the desired amount in case of a moving target).
Such a sighting device was disclosed by Budden et al. (U.S. Pat. No. 4,390,276) and consists of a solid block of glass with plane parallel opposite end faces. A partially reflecting concave surface in the block forms an image at infinity of a graticule which is illuminated by light entering the block through a window.
While the Budden sight has many of the above described advantages, it is limited in that it cannot be used under bad light conditions, not to speak of at dark. Other known gun sights based on the superposition principle have attempted to solve this problem by using a light source such as a miniature bulb to illuminate the graticule, with a battery as power source. Batteries, however, are known to go flat, and/or bulbs to burn out, at critical moments, and contacts and switches, especially of low-voltage circuits, are prone to fouling, especially under field conditions.
It is one of the objects of the present invention to overcome the problematic aspects of the prior-art sights and to provide a sighting device that can be used under any light conditions, uses for graticule illumination a self-energized, radio-luminescent light source of practically unlimited service life, and produces a superimposed aiming point that is clearly visible not only under bad light conditions, but even in full sunlight.